lightningd/json: make wallet_tx functions take amount_sat.

Using param_tok is generally deprecated, as it doesn't give any sanity checking
for the JSON 'check' command.  So make param_wtx usable directly, and
also make it have a struct amount_sat.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/json.c

@@ -10,6 +10,7 @@
 #include <common/memleak.h>
 #include <common/param.h>
 #include <common/type_to_string.h>
+#include <common/wallet_tx.h>
 #include <common/wireaddr.h>
 #include <gossipd/routing.h>
 #include <lightningd/json.h>